Sperm recognize siblings and pay it forward

Amazingly scientists have observed sperm cooperating like bicycle racing teammates. They apparently draft and also link themselves together to swim in tandem.

Once inside a female deer mouse's vagina, deer mouse sperm cells can discern, and hook up with, their brethren via structures on their heads. The cells "can then draft, Lance Armstrong-style, moving faster than they could alone thanks to more 'engine' power from the cluster," reports study co-author Heidi Fisher, an evolutionary geneticist at Harvard University's Hoekstra Laboratory of Mammalian Evolutionary Genetics.

Fisher earned her Ph.D. at Boston University and is currently studying the role of mating choice and sperm competition (and their underlying genetic basis) in deer mice. Heidi is funded by a 3-year NIH NRSA Postdoctoral Fellowship.

In some species where females mates with multiple males, groups of sperm join forces in order to outswim their uncooperative competitors. We've shown that in deer mice, cooperation only occurs among close relatives -- sperm from the same male.

Fisher's findings build on research published in 2002 by Harry Moore and colleagues at the University of Sheffield. "Moore found that sperm from wood mice could clump together to increase swimming velocity during their migration towards the egg, but did not identify kinship as the factor determining which spermatozoa join forces."

The mechanism that permits sperm to recognize their scrotum-mates is as yet undetermined and will be the subject of future research.